Unit load conveying apparatus

ABSTRACT

Disclosed is an apparatus for moving unit loads along an unpowered roller conveyor. The apparatus includes a drum, moved by power means along the conveyor path, and which engages and, in effect, attaches itself to the load when moving in one direction and engages but slips past the load, without attaching itself, when moving in the other direction. The drum is mounted for angular movement about an axis offset from the central axis of the drum so that when the drum, moving in one direction as a result of a horizontal force applied to it, engages the load, the force moment applied to the angular movement-axis of the drum merely swings the drum angularly away from the load and, when the drum is moved in the opposite direction, tends to swing the drum angularly toward the load, this resulting wedging action tending to lift the load and decrease the normal pressure acting between the load and the adjacent support surface, such as the conveyor rollers. When this normal force, multiplied by the coefficient of friction between the load surface and the support surface, is overcome by or falls below (as a result of the lifting action) the horizontal force applied to the drum, the drum will move the load horizontally. By controlling the travel of the drum along the length of the roller conveyor, a series of unit loads can thus be moved, sequentially or one-by-one, along the conveyor.

United States Patent [191 Bennett et al.

[ UNIT LOAD CONVEYING APPARATUS [75 Inventors: Harry L. Bennett, Richard E.

Stockton, both of Indianapolis, ind.

[73] Assignee: Economation Inc., Indianapolis,

Ind.

[22] Filed: Sept. 5, 1972 [21] Appl. No: 286,459

Primary Examiner-Evon C. Blunk Assistant Examiner-Hadd Lane Att0rneyMaurice A. Weikart [57] ABSTRACT Disclosed is an apparatus for moving unit loads along an unpowered roller conveyor. The apparatus includes Oct. 30, 1973 a drum, moved by power means along the conveyor path, and which engages and, in effect, attaches itself to the load when moving in one direction and engages but slips past the load, without attaching itself, when moving in the other direction. The drum is mounted for angular movement about an axis offset from the central axis of the drum so that when the drum, moving in one direction as a result of a horizontal force applied to it, engages the loadfthe force moment applied to the angular movement-axis of the drum merely swings the drum angularly away from the load and, when the drum is moved in the opposite direc tion, tends to swing the drum angularly toward the load, this resulting wedging action tending to lift the load and decrease the normal pressure acting between the load and the adjacent support surface, such as the conveyor rollers. When this normal force, multiplied by the coefficient of friction between the load surface and the support surface, is overcome by or falls below (as a result of the lifting action) the horizontal force applied to the drum, the drum will move the load horizontally. By controlling the travel of the drum along the length of the roller conveyor, a series of unit loads can thus be moved, sequentially or one-by-one, along the conveyor.

22 Claims, 9 Drawing Figures UNIT LOAD CONVEYING APPARATUS BACKGROUND OF THE INVENTION For rectilinear, relatively short (of the order of 150 feet, for example) roll conveyors, such as used to load or unload automatic machinery, store incoming merchandise, or the like, it is customary to utilize either gravity roll or power roll conveyors. These conveyors function to move unit loads (here used to refer to the handling of boxes, bags, packaged materials, castings, paper rolls and, in general, integrated items as distinguished from pulverized, granular and lumpy bulk materials) in a generally satisfactory manner. However, gravity roll conveyors encounter difficulties in providing for reverse travel of the load on the conveyor thus limiting the flexibility of their use and powered roll conveyors, while reversible, have the disadvantage of being relatively costly and do not lend themselves to sequential transport of a stack or series of unit loads. Both prior art systems thus have disadvantages, particularly for simple, relatively short, straight line conveyor applications.

The concept of the present invention provides a relatively inexpensive apparatus for sequentially moving, one-by-one or in multiples, a series of unit loads along a conveyor. The apparatus is of relatively simple, trouble-free construction which by use of limit switches, photocells or other control devices, lends itself very well to automatic or untended operation, repeating excursions along the conveyor path to move the load or loads from one station to another. Since, as previously pointed out, the initial action of the mobile member or drum is to tend to lift the load, decreasing its effective weight with respect to the supporting surface, and because of the mechanical advantage inherent in the wedging action of the eccentric or offset mounting of the drum, much heavier loads can be moved by a given horizontal force applied to the mobile member; much less force is required to move the load than would be required if the force were applied directly to the load. The power input can thus be less than required in conventional systems, and need only be sufficient to move a single increment or unit load in a stack or series of such loads since the apparatus will, when properly controlled, pick up and move only the first or end increment in a series of line-up of unit loads. A slip-friction connection between the drum periphery and the central, axial shaft of the drum prevents overloading of the apparatus. While the apparatus has been described in the environment of roll type conveyors, it also has advantages in moving flat, pallet type, rigid surface loads (such as steel sheets, bundles of plywood sheets, etc.).

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a roller conveyor system utilizing the apparatus of the present invention.

FIG. 2 is a fragmentary, perspective view of the conveyor system of FIG. 1 and illustrating the orientation of the mobile member with respect to the conveyor rollers.

FIG. 3 is a side view of the mobile member illustrated in FIG. 2.

FIG. 4 is a side view of the drum component of the mobile member.

FIG. 5 is a fragmentary, schematic, side view of the mobile member approaching a series of unit loads on a conveyor.

FIG. 6 is a view similar to FIG. 5 but illustrating the action of the apparatus when the direction of motion of the mobile member is reversed.

FIG. 7 is a view similar to FIG. 5 but illustrating the approach of the mobile member to a conveyorsupported unit load when the counterweight has been positionally shifted with relation to the position of the drum component.

FIG. 8 is a schematic view of a, portion of the apparatus further illustrating its operation.

FIG. 9 is a schematic view of a structure substantially equivalent mechanically to the structure of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring initially to FIGS. 1 and 2, a straight-line conveyor path is illustrated schematically at 10, the

conveyor having rollers 11 and supporting a series of unit loads indicated at 12. The construction so far described is, of course, conventional. The apparatus of the present invention includes a mobile member indicated generally at 13 which is adapted to travel along a track 14 extending parallel to and closely adjacent the conveyor path 10. The mobile member is moved in either direction along its path of movement (established by the track 14) by means of an endless cable 16 which, at one end passes over an idler wheel 17 and at its other end around a drive member 18. The drive member 18 is powered by a speed reducer '19 driven by an electric motor 21. The motor may be of the reversible type with its direction of rotation being controlled by a switch 22 operated by a control member 23. Power may be supplied to the motor through the wires 24. The control member 23 may take the form of limit switches which are operated at each end of the travel of the mobile member or at selected points along its path, or may take the form of photoelectric devices, probe actuated switches or similar electric sensing means. 7

As may be seen in FIG. 2, the unpowered roller conveyor 11 is preferably formed by two parallel flights of rollers indicated at 12a and 12b with the mobile member 13 and its track 14 positioned in the space between the two parallel roller flights. It will be understood that the conveyor might take the form of two spaced, stationary rails on which the load rests rather than the spaced roller flights 12a and 12b. The mobile member includes a frame composed of side plates 26 and 27, upper transverse members 28 and 29 and lower transverse members 31. The cable 16, as illustrated in FIG. 2, may be attached to the upper transverse members 28 and 29. The frame journals front and rear wheels 32 which have'a grooved periphery and which ride the track 14. The mobile member also is provided with a drum component, indicated generally at 33 in FIG. 2 and shown in detail in FIGS. 3 and 4.

Referring to FIGS. 3 and 4, the drum 33 is formed by a tubular, cylindrical member 34 whose periphery is provided with a frictional surface such as the serrated rubber face indicated at 36 in FIG. 4, the serrated surface of the drum also being visible in FIG. 2. As may best be seen in FIG. 4, a central flange 37 extends radiallyinwardly within the drum and the flange is grasped by the frictional facing members 38 of a conventional friction clutch 39 providing a slip-friction connection between the drum periphery and a central shaft 41 defining the central, longitudinal axis of the drum. The

cylindrical drum 34 provides a load-engaging element which is generally circular in cross-section. Friction clutch 39 is not shown in detail herein since it is of conventional, known construction.

As will be evident from FIG. 4 the central shaft 41 extends beyond the ends of the drum and, as will'be evident from FIG. 3, is keyed, as indicated at 42, to a circular flange 43 extending from the face of a disc 44. While only one disc 44 and shaft attachment 42 are shown in FIG. 3, it will be understood that a duplicate structure (disc, and supporting members) is carried by the opposite extending end of the shaft, the general arrangement being evident from FIG. 2 in which both discs 44 appear. Rollers 47, journalled on pins 48 which extend from the frame side members engage the periphery and support the discs 44 for angular movement about their center 46 (FIG. 3). It will be noted that the center of the discs 46 is offset sidewardly from the central longitudinal axis 47 (FIG. 3) of the drum and that the mounting of the discs 44 is such that their center of rotation 46 forms an eccentric axis of angular motion for the load-engaging element which takes the form of the drum 33.

The discs and drum are held in a neutral position, that is, a position in which the axes 46 and 47 are generally horizontally aligned, by means of a counterweight 51 which extends across the roller and is carried at the outer end of arms 52. The arms 52 are pivotally supported on pins 53 which extend inwardly from the inner face of the discs 44, the pivotal support pins 53 being on the opposite side of the angular motion axis 46 from the center 47 of the shaft 41. The position of the counterweight 51 shown in FIG. 3 is determined by engagement of the arms 52 with abutments or stops 54 which extend inwardly from the inner face of the discs and act as stops against which the arms 52 rest.'The mass of the counterweight 51 and its position with respect to the axis of angular motion 46 is such as to balance the center of mass of the, in effect, eccentrically mounted drum 33. Stop abutments 56, identical to the stop abutments 54 also extend from the inner face of the discs and serve to define a second position for the counterweight 51 in which the arms52 are engaged by the abutments 56. Swinging the counterweight and arms 52 counterclockwise, as viewed in FIG. 3, until the arms 52 rests against the abutments 56 serves to rotate the disc and drum counterclockwise so that the portion of the disc and drum farthest from the axis of angular motion 46 is on the opposite, or right hand (as viewed in FIG. 3), side of the axis 46, this reversal of position of the counterweight and drum being illustrated by a comparison of FIGS. 6 and 7.

Referring to FIGS. 5, 6 and 7, operation of the apparatus will now be described. In FIG. there is shown an array or series of unit loads 12 resting at one end of the roller conveyor and which are to be transported in a leftward direction (as viewed in FIG. 5) to a station, for example, at the opposite end of the conveyor path. If it is assumed that the power means 21 of the mobile member 13 is moving it toward the first unit load in the line, that is, in the direction of the arrow indicated at 61 in FIG. 5, the mobile member taking the form of roller 34 will be in its solid line position of FIG. 5. In such position the major portion of the cross section of the drum 34 will be on the side of the axis of angular movement 46 away from the unit loads. Further motion of the mobile member in the direction indicated by the arrow 61 in FIG. 5 (in which axis 46 leads the drum axis 47) will cause the roller 34 to engage the underside of the load, such initial engagement position of the drum being indicated in broken lines identified at 71 in FIG. 5. As the drum moves further rightwardly to its broken line position indicated at 72, engagement of the load with the periphery of the drum causes the load to angularly swing the drum downwardly about the axis of angular motion 46. This downward swing of the drum, permitting it to pass under the load, results from the reactive force of the load applied, in effect, to the drum in the direction of arrow 73, which swings the drum downwardly about axis 46. The drum 34 may thus slip easily beneath the load until it reaches a desired position such as its broken line position 72 wherein the drum is centrally located beneath the load.

If the direction of motion of the mobile member 13 is now reversed, as indicated in FIG. 6 by a force whose direction is indicated by the arrow 76, the drum 34 will progress horizontally from its solid line position to its broken line position indicated at 77 in FIG. 6. In moving to this position, that is, when the direction of movement of the drum is reversed so that axis 46 trails the drum axis 47, the drum will initially tend to swing upwardly, or clockwise'(as viewed in FIG. 6), under the load. The mechanical advantage inherent in the resulting wedging action (explained more fully subsequently with reference to FIGS. 8 and 9) will cause the horizontal force, constantly applied in the direction of arrow 76, to thus apply a substantial lifting force upwardly under the load, indicated by arrow in FIG. 6. This upward force acts against the weight of the load and thus decreases the pressure between the load and the supporting surface, in this case, the rollers of the conveyor. Since this load-to-support surface pressure, acting normal to the support surface, is the factor which, multiplied by the appropriate coefficient of friction, measures the force necessary to start and move the load along the support surface, as the effective weight of the load decreases a point is reached when the constantly applied horizontal force exceeds the product of the appropriate coefficient of friction and the effective weight of the load. At this point the load will begin to move horizontally with mobile member 13. The action of the apparatus is such that an increasing lifting force is applied to the load until the load begins to move horizontally and thereupon the lifting force ceases to increase and the force applied to the mobile member 13 is utilized in producing motion of the load along the supporting surface. Since the coefficient of friction of rest is greater than that of motion, there is a snapaction effect in that after motion of the load is initiated, less motive power input to the mobile member is necessary to maintain the motion and slipping cannot occur once motion has begun. The load 12 will be moved with the drum through a position indicated by broken line 79 and the drum through its position indicated by broken line 77. Further movement of the mobile member 13 leftwardly, as viewed in FIG. 6, causes the drum to pull the load further along the conveyor to the station at which the load is to be deposited, such further mothese move rightwardly as viewed in FIGS. 5 and 6, the load is immediately freed from the drum. Repeated movement of the mobile member rightwardly to pickup the initial one of the unit loads in the alignment and transport of the load to the desired station at the leftward end of the roller conveyor (as viewed in FIGS. 5 and 6) results in the sequential transport of the unit loads from their initial position to the subsequent station or position on the roller conveyor. By causing the control means 23 for the direction of motion of the mobile member 13 (FIG. 1) to take the form of a limit switch actuated at each end of the travel path of the mobile member, such sequential transport of the unit loads can be performed automatically.

The direction around the conveyor path in which the unit loads may be moved by the mobile member can be reversed, that is, changed from the direction of load movement described with reference to FIGS. 5 and 6, by shifting the position of the counterweight 51 so that the arms 52 (FIG. 3) carrying the counterweight rest against the stops 56, rather than the stops 54. When the counterweight 51 is moved to this new position, the drum 34 will move to the position shown in FIG. 7 wherein the major portion of the drum cross section is on the opposite side of the axis of angular movement 46 from that shown in FIGS. 5 and 6. Under these conditions, when the mobile member 13 is moved leftwardly (as viewed in FIG. 7) in the direction indicated I by the arrow 91 in FIG. 7, engagement of the drum periphery by the underside of the load will swing the drum downwardly about the axis of angular movement 46 permitting the drum to move easily along the undersurface of the load. When the direction of the motion of the mobile member is reversed, that is, changed from left to rightward as viewed in FIG. 7, the drum will apply a force tending to lift the load until the load starts to move, the power input to the mobile member then being utilized in moving the load horizontally, as described with reference to FIG. 6. The counterweight 51 thus provides a positionally shiftable member for selectively reversing the position of the axis of angular movement 46 for the drum with respect to the central longitudinal axis 47 of the drum and thereby providing a means for selecting the direction in which a unit load is moved by the mobile member along the conveyor path. 7

An explanation of the wedging action, hence the mechanical advantage, achieved with the apparatus is illustrated in FIGS. 8 and 9. Referring specifically to FIG. 8, as a force is applied to mobile member 13 in the direction of arrow 91, the tendency of drum 34 to move angularly about axis 46, in effect, moves a wedge, having a height H and a length L, beneath the load 12. FIG. 9 illustrates the equivalent arrangement in a rectilinear mode, the weight of load 12 being there indicated by W. Referring to the schematic illustration of FIG. 9, it will be evident that the force necessary to drive the wedge beneath the load is a direct function of the ratio of H to L multiplied by the load weight W. Since the ratio of H to L, illustrated in FIG. 9, is substantially less than unity, the wedge-driving force required is only a fraction of the load weight W. The upward force on the necessary to'move the load horizontally along the support surface. When the force necessary to move the load along the support surface has decreased (because of the wedging action) to a value less than the force applied to the mobile member 13, the load will be moved along the support surface by the mobile member. The force applied to the mobile member thus tends to lift the load until the frictional force resisting motion of the load along the conveyor or lock supporting surface is overcome.

From the foregoing it will be evident that the apparatus of the present invention provides a relatively inexpensive and reliable transporting means for use with conveyors particularly where straight flow conveyor lines are used to handle accumulative unit loads. The apparatus is effective for use with sliding pallets on skids or, in general, upon any rigid surface load which is to be moved along a supporting surface. The amount of upward force applied in lifting the load can be varied by varying thedistance between axis 46 and drum center 47, that is, by varying the H to L ratio of FIGS. 8 and 9. The power means, such as motor 21 musthave a power input only sufficient to move a single unit load, not an accumulated group of unit loads, and much heavier loads can be handled with a given power input because of the lifting action and mechanical advantage provided by the eccentric mounting of the drum. The slip-friction connection between the drum periphery and its central shaft limits the force that can be exerted by the drum on the load and thus prevents overloading of the power means. This slip connection may, of course, be adjustable to vary, within limits, the point at which the friction clutch will slip.

We claim:

1. Transport apparatus for moving a rigid faced load along a load-supporting surface, said apparatus comprising a mobile member for engaging the rigid face of the load, means establishing a path of movement for said mobile member along said load-supporting surface, power means for moving said mobile member, said mobile member carrying a load-engaging element having surface adapted to engage the rigid face of the load and mounted for angular motion about an axis which is offset laterally from said load face engaging surface of the element, the resulting wedging action of said element with respect to the load, when said mobile member is moved in a direction such that said load face engaging surface of the element, leads said angular motion axis, tending to lift the load until the frictional force resisting motion of the load along said loadsupporting surface is overcome.

2. Transport apparatus as claimed in claim 1 in which said load supporting surface takes the form of a roll type conveyor and said rigid face of the load rests on the conveyor rolls.

3. Transport apparatus as claimed in claim 1 in which said means establishing a path of movement for the mobile member takes the form of a track rail, and said mobile member is provided with supporting elements riding said track rail.

4. Transport apparatus 'as claimed in claim 1 in which said load-engaging element has a generally cylindrical configuration with its central axis transverse to the movement path of the mobile member and parallel to said angular motion axis and its outer convex face provides said surface adapted to engage the rigid face of the load.

5. Transport apparatus as claimed in claim 4 in which there is a slip-connection between the load engaging convex outer surface of said element and its central axis.

6. Transport apparatus for moving unit loads sequentially along an unpowered conveyor path, said apparatus comprising a mobile member for engaging and attaching itself to a unit load on the conveyor path, means establishing a path of movement for said mobile member parallel to and closely adjacent said conveyor path, power means for moving said mobile member in either direction along its said path of movement, said mobile member having a load-engaging element which is generally circular in cross-section and mounted for angular motion about an axis transverse to the path of movement of said mobile member and offset laterally from the center of said element, said element having a friction surface on its periphery adapted to engage a stationary unit load on said conveyor path, said element moving along the surface of said stationary unit load when said mobile member is moved in a direction such that said center of the load-engaging element trails said axis of angular motion, and when moved in a direction in which said element center leads said axis of angular motion the resulting wedging action of said element with respect to the load tending to lift the load until the frictional force resisting motion of the load along said conveyor path is overcome.

7. Transport apparatus as claimed in claim 6 in which said unpowered conveyor path is formed by two parallel flights of rollers with said means establishing a path of movement for the mobile member interposed between said roller flights.

8. Transport apparatus as claimed in claim 7 in which said means establishing a path of movement for the mobile member takes the form of a track rail, and said mobile member is provided with supporting elements riding said track rail.

9. Transport apparatus as claimed in claim 8 in which said power means for moving the mobile member takes the form of an endless cable generally coextensive with said track rail and an electric motor adapted to move said cable.

10. Transport apparatus as claimed in claim 9 in which control means is provided for said motor for reversing the direction of the cable motion, and hence of the movement of said mobile member, at preselected points in the travel of the mobile member.

11. Transport apparatus as claimed in claim 6 in which there is a slip-connection between the friction surfaced periphery of said load engaging element and its said angular motion-axis to prevent overloading said power means and to limit the motive force exerted on the unit load engaged by said element.

12. Transport apparatus as claimed in claim 11 in which said load-engaging element takes the form of a generally cylindrical drum with said center of the element lying on the central longitudinal axis of the drum.

13. Transport apparatus as claimed in claim 12 including a positionally shiftable member for selectively reversing the position of said axis of angular movement for the drum with respect to said central longitudinal axis of the drum, to thereby select the direction in which a unit load is moved by said mobile member along the conveyor path.

14. Transport apparatus as claimed in claim 13 in which said positionably shiftable member takes the form of a counterweight supported on an arm pivotally attached to said drum, the axis of angular movement of the drum, the central longitudinal axis of the drum and the pivotal attachment of said arm to the drum all being diametrically aligned across the end of the drum.

15. A mobile member for load transfer adapted for motion adjacent an unpowered roller conveyor and for attaching itself to unit loads on the conveyor and moving them along the conveyor path, said mobile member comprising a frame, a cylindrically shaped drum extending across the frame transverse to the direction of motion of the mobile member and adapted to engage the underside of a unit load on the conveyor, a drumsupporting shaft extending centrally through the drum, the extending opposite ends of said shaft each carrying a disc rigidly mounted thereon with the axis of the shaft offset from the center of the discs, support means on said framefor supporting said discs for angular movement about their center, the eccentric mounting for said drum thus provided permitting said drum to move along the underside of the load as said frame moves in one direction, the wedging action of said drum with respect to said load when said frame moves in the opposite direction tending to lift the load until the frictional force resisting motion of the load along said conveyor path is overcome.

16. A mobile member as claimed in claim 15 in which said support means for said discs comprises spaced rollers carried by said frame and accommodating the circular periphery of said discs.

17. A mobile member as claimed in claim 15 which is adapted for motion by wheels supporting said mobile member frame and a track accommodating said wheels which extends parallel to and closely adjacent said roller conveyor, and power means for moving said mobile memberin either direction along said track.

18. A mobile member as claimed in claim 15 in which the peripheral, load-engaging surface portion of said drum has a slippable connection with said supporting shaft.

19. A mobile member as claimed in claim 15 in which at least one of said discs carries a counterweight providing a force moment about said angular motion-axis of'the discs which balances the force moment about said axis produced by the offset mounting of-said drum shaft axis.

20. A mobile member as claimed in claim 19 in which said counterweight takes the form of an elongated member of substantial mass extending parallel to said drum and supported by arms extending chordally from said discs.

21. A mobile member as claimed in claim 20 in which said counterweight supporting arms are pivotally connected to their respective discs to permit said counterweight to be shifted in position with respect to said angular motion-axis thereby reversing the positional relationship between said angular motion axis and. send drum shaft axis.

22. A mobile member as claimed in claim 21 in which at least one of said discs carries spaced abutments adapted to be selectively engaged by a counterweight arm to define two alternate positions for said arms with respect to said discs.

* i l ll 

1. Transport apparatus for moving a rigid faced load along a load-supporting surface, said apparatus comprising a mobile member for engaging the rigid face of the load, means establishing a path of movement for said mobile member along said load-supporting surface, power means for moving said mobile member, said mobile member carrying a load-engaging element having surface adapted to engage the rigid face of the load and mounted for angular motion about an axis which is offset laterally from said load face engaging surface of the element, the resulting wedging action of said element with respect to the load, when said mobile member is moved in a direction such that said load face engaging surface of the element leads said angular motion axis, tending to lift the load until the frictional force resisting motion of the load along said load-supporting surface is overcome.
 2. Transport apparatus as claimed in claim 1 in which said load supporting surface takes the form of a roll type conveyor and said rigid face of the load rests on the conveyor rolls.
 3. Transport apparatus as claimed in claim 1 in which said means establishing a path of movement for the mobile member takes the form of a track rail, and said mobile member is provided with supporting elements riding said track rail.
 4. Transport apparatus as claimed in claim 1 in which said load-engaging element has a generally cylindrical configuration with its central axis transverse to the movement path of the mobile member and parallel to said angular motion axis and its outer convex face provides said surface adapted to engage the rigid face of the load.
 5. Transport apparatus as claimed in claim 4 in which there is a slip-connection between the load engaging convex outer surface of said element and its central axis.
 6. Transport apparatus for moving unit loads sequentially along an unpowered conveyor path, said apparatus comprising a mobile member for engaging and attaching itself to a unit load on the conveyor path, means establishing a path of movement for said mobile member parallel to and closely adjacent said conveyor path, power means for moving said mobile member in either direction along its said path of movement, said mobile member having a load-engaging element which is generally circular in cross-section and mounted for angular motion about an axis transverse to the path of movement of said mobile member and offset laterally from the center of said element, said element having a friction surface on its periphery adapted to engage a stationary unit load on said conveyor path, said element moving along the surface of said stationary unit load when said mobile member is moved in a direction such that said center of the load-engaging element trails said axis of angular motion, and when moved in a direction in which said element center leads said axis of angular motion the resulting wedging action of said element with respect to the load tending to lift the loAd until the frictional force resisting motion of the load along said conveyor path is overcome.
 7. Transport apparatus as claimed in claim 6 in which said unpowered conveyor path is formed by two parallel flights of rollers with said means establishing a path of movement for the mobile member interposed between said roller flights.
 8. Transport apparatus as claimed in claim 7 in which said means establishing a path of movement for the mobile member takes the form of a track rail, and said mobile member is provided with supporting elements riding said track rail.
 9. Transport apparatus as claimed in claim 8 in which said power means for moving the mobile member takes the form of an endless cable generally coextensive with said track rail and an electric motor adapted to move said cable.
 10. Transport apparatus as claimed in claim 9 in which control means is provided for said motor for reversing the direction of the cable motion, and hence of the movement of said mobile member, at preselected points in the travel of the mobile member.
 11. Transport apparatus as claimed in claim 6 in which there is a slip-connection between the friction surfaced periphery of said load engaging element and its said angular motion-axis to prevent overloading said power means and to limit the motive force exerted on the unit load engaged by said element.
 12. Transport apparatus as claimed in claim 11 in which said load-engaging element takes the form of a generally cylindrical drum with said center of the element lying on the central longitudinal axis of the drum.
 13. Transport apparatus as claimed in claim 12 including a positionally shiftable member for selectively reversing the position of said axis of angular movement for the drum with respect to said central longitudinal axis of the drum, to thereby select the direction in which a unit load is moved by said mobile member along the conveyor path.
 14. Transport apparatus as claimed in claim 13 in which said positionably shiftable member takes the form of a counterweight supported on an arm pivotally attached to said drum, the axis of angular movement of the drum, the central longitudinal axis of the drum and the pivotal attachment of said arm to the drum all being diametrically aligned across the end of the drum.
 15. A mobile member for load transfer adapted for motion adjacent an unpowered roller conveyor and for attaching itself to unit loads on the conveyor and moving them along the conveyor path, said mobile member comprising a frame, a cylindrically shaped drum extending across the frame transverse to the direction of motion of the mobile member and adapted to engage the underside of a unit load on the conveyor, a drum-supporting shaft extending centrally through the drum, the extending opposite ends of said shaft each carrying a disc rigidly mounted thereon with the axis of the shaft offset from the center of the discs, support means on said frame for supporting said discs for angular movement about their center, the eccentric mounting for said drum thus provided permitting said drum to move along the underside of the load as said frame moves in one direction, the wedging action of said drum with respect to said load when said frame moves in the opposite direction tending to lift the load until the frictional force resisting motion of the load along said conveyor path is overcome.
 16. A mobile member as claimed in claim 15 in which said support means for said discs comprises spaced rollers carried by said frame and accommodating the circular periphery of said discs.
 17. A mobile member as claimed in claim 15 which is adapted for motion by wheels supporting said mobile member frame and a track accommodating said wheels which extends parallel to and closely adjacent said roller conveyor, and power means for moving said mobile member in either direction along said track.
 18. A mobile member as claimed in claim 15 in which the peripheral, load-engaging surface portion of said drum has a slippAble connection with said supporting shaft.
 19. A mobile member as claimed in claim 15 in which at least one of said discs carries a counterweight providing a force moment about said angular motion-axis of the discs which balances the force moment about said axis produced by the offset mounting of said drum shaft axis.
 20. A mobile member as claimed in claim 19 in which said counterweight takes the form of an elongated member of substantial mass extending parallel to said drum and supported by arms extending chordally from said discs.
 21. A mobile member as claimed in claim 20 in which said counterweight supporting arms are pivotally connected to their respective discs to permit said counterweight to be shifted in position with respect to said angular motion-axis thereby reversing the positional relationship between said angular motion axis and send drum shaft axis.
 22. A mobile member as claimed in claim 21 in which at least one of said discs carries spaced abutments adapted to be selectively engaged by a counterweight arm to define two alternate positions for said arms with respect to said discs. 